Electric motor control system



CROSS EFESL EXAMINER JKM 5, 1951 G. s. cARRlcK 2,555,674

ELECTRIC uo'roR CONTROL sysma Filed My 1o, `1945 4 sheets-sheet 2 CROSS REFERC t/Jwlllib June 5, 1951 G. s. cARRlcK 2,555,674

ELECTRIC MOTCR CONTROL SYSTEM Filed May 10, 1945 l 4 Sheets-Sheet 3 All annessa* i z s l l l l s f,

lll/1111111111114' i? y I,11111111111 zz 1 l 'f l l nml e Y A O 3 /34 y Dfw Vp paratus, and more particularly to pressure re ations oi which are employed to provide the desiredj-l'egulatmn- :f2 5. Kentmere-regulators of this type have em- Aresponse to variations in the heightof the liquid In one 4embodiment of my invention the switch- Patentea June 5, n @Riagg UNITED- ...SirATES rarest OFFICE- I Y I 3 AGerald S. Carrick,

1 Mutation May 1n, 1945, serial Nessun f claimsg' (cll'cisg-sif' A. .2

ably also the light sourcesa're arranged to be movedvertically in response to activation'of,. t'.he 0611s. .S es. t0 .followithe .changes in liquid leveli morder to prevent over-'regulation-andhunting In accordance withwanother embodiment Icimyinvention, `magnetically responSiYQf-'electric switches are spaced vertically beside-afmanomo etertube. A- magnet isarranged-to iloatat the p loyed a float responsive' to variation in the.l level surface oi' the liquidin the -tube3and-hence moves of a mercury column in a manometer.I However, up and down with variations .'in'liquid level -so as Ln such an apparatus the iloat is apt to stick, thus to alter the magnetic Atorce or. ilux which-passes resulting in improper-regulation.V v`vIn addition the through the wall of the tube tothe respective noat -must bey placed -in the atmospheric `leg vof switches,4 vAis'in the first embodiment mentioned, themanometer in order that the motion thereof the switches are mounted so as to be moved'vermay be transmitted to outside the :nanometer l5' tically in `response t0 the completion and interwithout requiring stuffing boxes or. the like, which ruption of the circuits therethrough so as to folmeans that it must belocated at a' relatively high low variations in liquid level and thus prevent elevation in the plant. y. Moreover, inasmuch as it over-regulation.1` .ff-Ggf c .www requires approximately two `inches of mercury Further objects ndadvantages of my invencolumn to balance 1 1b.. of pressure, the atmos 20 tion will be apparent from the following descrippheric legmust be unreasonably long if the prestion, considered in connection. with the accomsure is high, as is the case in modern steam plants panying drawings which form apart of the speciemploying steam pressure up toandabove 2,000 vflcation and of which: i lbs. per square inch, which would require an Fig. 1 is a more or less diagrammatic view of an atmospheric leg approximately 333 feet in height. embodiment of my invention employing photo- In accordance with my invention, I employ electric cells and in which the. pressureds balf electricswitching means located adjacent to and anced solely by a col\ 1mn .'f4 mercury or otherl outside either legof= amanometer, thev switching suitable liquidmr2-'f means lbeing responsive toV the transmission of E fFig. .2 is a diagrammatic view of my invention energy through the wall of the tube, together with 3o embodied in an apparatus wherein the pressure vmeans for'varying such transmission of energy in is balanced in part by a loadeddiaphragm; 5; o Fig. 3 is a more or'less diagrammatic view oimy column in the leg. Inasmuch as no moving parts invention in a system in which the pressure is balpass through or, into the manomter tube, the anced in part by a body of trapped gas; g .f electricl switching means may be controlled by the 4 is a more or less diagrammatic view of level .of the ymercury .or other liquidV in the presmy invention `inwhich the pressureis .balanced sure legof the'inanometer. Consequently, even J if theentire" steam orgother pressure is .balanced r Fig. 5 is amore or less diagrammatic view of by a'me'rcury column, the regulating apparatus an embodiment involving Switchingrmean' may be located, if desired, at a relatively low level 40 sponsiveto variations in magnetic flux.A pyf5-r; in the plant. Moreover, it is possible to use'vari- Referring more particularly to Figflyreferous novel'means 'for balancing'a, portionof the ence character ludesignates a conduit such as pressure, thereby makingV unnecessary exthe steam header ina power plant, which .carries tremelylong atmospheric leg,l y Y ij., f fluid under pressure, the variations in which pres- `lilly invention alsoV includes lnovel follow-up sure are to be utilized for regulating purposes, for mechanism' 'for preventing over-regulation. v.instance for regulating the rate of steam generav ,tion as by controlling the draft, therate of-fue1 ing means kcomprises' a pair ofrvverticallyspaced feed, or other factors, as iswell known Yin power photo-electric cells on one side of a transparent iplant operation.; Connected to the header l0 is `inanometefrA tube. Suitable light vsources are ar- 5 0 A a conduit I2, in which is preferably interposed a ranged to direct beams of light through the tube shut-off valve ni4, and which leads to the upper .to the Cells, variations in liquidlevel thus serving ,end of a transparent, preferab1ycy1lndrica1 conto make and break' the .beams which in turn -tainer I 76, which in all respects may be similarto 4causes `completion and interruption of electric a gauge glass and will be referred to as such here- My invention relatesto pressure responsive apsponsive regulators, and especially those employing:a column of liquidgsuch as mercury, to balyance or partially balance the pressure, the vari- 5 in part bya loadedbellows; andum@ er f,

srcuitsillgellshthejseilsarlhe.sella.eee Prefer; The conduit la v-communieatei with. .the

ifi-ir A employed in the manometer. opaque, which is desirable, as will hereinafter apmuch as mercury is the heaviest substance which` is liquid at normal temperature, it is preferably Kiso, 'mercury is pear. However, it is within the scope of my invention to employ other liquids, auch' his water,

particularly if the pressure is low. A mercury trap 22 of any well-known construction may be provided at the upper open end of the atmospheric leg TD in 'order to catch mercury which would be blown out as the result of an abnormal increase in the pressure in line I0, or as a result o! lnsumcicnt mercury in the 'manometer vwhich would cause eHow-through.' g"

' suitably meuntedadjacent to the'gauge glass (61 is a housing 24 within which 'is reciprocally mounted a rod 26. This'rod preferably has a square or other vnow-circular cross-section so as to preventmtation thereof in the housing. A' portion of the rod ls formed with an external serewthread 28 which engages a similar internal thread formed in the gear 60. "This gear jis rotatably mountedin the housing 24, by means of combined radial and thrust bearings 32. The rod 26 has rigidly attached thereto an arm 34 which is lorked' so las to provide an upperarm 36 and a lower arm 38. Both of these ar'ms have arcuate portions which extend around the outside -of the gauge glass i6 so 'that one endof the arcuate por-tion of each arm ls diametrlcally pposite the other end with respect to the glass. A photoelectric cell 40 is suitably mounted on one end of the lupper'arm 36, while a similar cell 42 is mounted on the correspondingend of the lower arm 3B. "The opposite tends of these arms carry light sources 44 and 46, respectively, each lof which may be provided with a suitable lensesystem as is diegrammatieally 'indicated at 46, which serves to'concentrate'beams of light from the light sources, and to direct the beams through Ehe-gauge glass I6 towards the respective photoelectric cells. Each 'of the latter vis preferably provided with a hood or the like 50, which serves to protect it from cxtraneouslight, including light from the wrong light source. In other words, the cell 42 should not receive light 'from the source 44, nor from any" other place than the source 46. Photo-electric cell 49 is connected in series through suitable flexible leads to a'battery `52 and the solenoid 54 ol' a l'elay 'having a normally Aclosed c ontacti.Y 'Photo-electric cell 42 is simillarlyY connected through lsuitaltile iiexible leads withthef battery 5 6 and the'jsOIenOid ofa relay 'having a'- normally open contact 62. Obviously, both of 'the relaylo'ircuiis could be connected in parallel tothe lsame battery, ort' nypther suit able source of electric energy@ J 'C' A reversible'electrio motor 64 carries a pinion 66 which meshes with the gear 60. This motor lsf'pr'ovided with three terminals, pf which terminal 68 is connected to the wire la of any suit'- able power circuit, while the terminals 'l2 and :14 are connectedto the other wire 78 of the circuit through the contacts 56 and 62, respectively.

As is well known, the internal connections of the motor are such that it will rotate in one direction when supplied with current through the terminals 68 and 12, and will run in the opposite direction when supplied with current through the terminals 68 and 14. The above described device operates as follows:

Assuming the valve I4 to be open, pressure existing in the header l0 will be exerted through the conduit I2 on the upper surface of the mercury, or other liquid, contained within the gauge glass I6 and will depress the level of the mercury therein, at the same time raising it in the atmospheric leg 26 until the diilerence in heads of the two mercury columns balances the pressure. The amount of mercury placed in the manometer is so chosen that the lever thereof in the pressure leg will stand at about the middle of the gauge glass when the pressure in the header I0 is normal, as is shown in Fig. 1. With the parts in the position shown in this gure, the beam of light from the source 44 will pass through the transparent gauge glass I 6 above the level ofthe mercury therein and will strike the photo-electric cell 40. The nature of this cell is such that, when subjected to light, it closes the electric circuit therethrough, thus energizing the solenoid 54 and maintaining the contact 56 open. On the other end, the light from the source 46 is in-- terrupted by the mercury in the gauge glass and consequently no light strikes the photo-electric cell 42 and hence the solenoid 66 is not energized. As a result the Contact s2 is open and die meter 6'4 is idle. Should the pressure in the header i6 increase, it will depress the level of the liquid in the gauge glass I6 until the level is below the beam of light from the source -46 and, hence, this beam will strike the cell 42, thus energizing the solenoid 60 and closing the contact 62. This connects the motor 64 to the power supply through the terminals 68 and 74, which causes the motor to rotate in the proper direction so as to move the rod 26 downwardly at a speed which is`preferably greater than the speed at which the mercury level is depressed as a result of normal iiuctuations of pressures M nasmuchas the light sources and the photoelectric cells are carried by the rod 26, they will move downwardly with it and the beam from the source 46 will be interrupted by the mercury in the gauge glass, thus opening Vthe contact 62 and stopping the motor. If the device is employed as a regulator, the downward movement of rod 26, through suitable transmission means, has eiected an adjustment 'of some member which tends to decrease the pressure in the line 10. If the regulation resulting from this down-` ward movement of the rod 26 has been sucient to arrest the increase in pressure, the level in the gauge glass does not decrease further and 'no further regulation takes place. However, 'if the pressure continues to increase, as soon as the mercury level falls below the beam4 from the source 46, contact 62 'is again ,closed and the motor operates to further lower the rod 26 and hence to produce further regulation for decreasing the `pressure. -This step-by-step regulation continues until the increase in 'pressure is arrested. The advantage of the step-by-step movement is that it prevents over-regulation and hence hunting 'of the device. Y In the event the pressure in the line l0 decreases, the mercury level in the gauge glass rises so as to interrupt the beam of light from the source 44, which in turn opens the circuit o! the Een - i'iliaphragm 8 2 raise the' rod 26. sources and the photo-electric scribed, 'so asA to raises the light cells until the beam from the source 44 'strikes the. 58 and stop-v this action is re#-l cell'40, thus opening the contacty ping the motor. If necessary, peated, in the same manner as described nection with the increase in pressure.

It will be moving parts extend through the pressure'leg of the manometer the regulatingapparatus'may b e located in the neighborhood oftheliquid level in 'this leg, which is always lower than the level in the atmospheric leg? Hence the apparatus may beplaced ata low elevation even if a relatively long atmospheric leg is required linfo'rder to balance the pressure. As a matter o I fact, the atmospheric'leg can extended through the roof of the plantV and up alongside thefstack in `order to enable it to balance very high vste'eun pressures.l In Fig. 2 there is'shown an embodiment of my invention in whichthe 'major portion ofthe pressureis balanced by means of'a loaded diaphragm, thus eliminating the necessity of a highatmosphericleg, and hence is particularly advantageous for use with,4 high pressures. Referring to the drawing,' condu it I2 which is connected to the header I and is provided with a shut-oil' valve I4, as was the case in Fig. l, com municates with a diaphragm chamber 80, the upper end of which is closed -by means -ofv a movable diaphragm 82. This diaphragm carries av knife edge 84 which cooperates `witha notch formed in the lever tjwhich is pivoted atene end at 88. The otherend of the leven-'carries' apreierably movable weight 90, t he position of which o n the lever arm may be sol adjusted that in conthe resulting force applied to the diaphragm 82v through the knife edge 84 is suii'icientto balance the major portion Vof thehuid pressurewithin the chamber 8|i. j Vjin 'Mounted above'the lever l|36 is a diaphragm chamber 92, the lower end of which is c losed by movable diaphragm. A943vyhicl'i carries apiznilfe edge 98 .which cooperatesv with a notch in the lever 8 6.4 ,The diaphragmchamber'SZ 'is'fconnected by means of conduits 98 and |00 with gauge glasses |02 and |04, respectively, which are located at the same level. The rod 28, which is moved up and down lbyjthe same mechanism as disclosed in liigflf'extends between the twp gauge glasses. v'Ihis'rcd Carries va lower hori-l zontal arm |06 which extends around the' ygauge glass |02, and v an lupper horizontal arm |08 which extends around theigaugfefglass I04. The 'upper arm carriesh'a photqfeleetric cell v4l),v a s ht Spurs@ 44 and? if deeifgfdre 'lens SYStem/'48? while the lower 'arm carries the'; photo-electric 42,; light source 4 6 and'le'nsfs'ystei 48."" 'Ihe imei ds 9f the'ga 111ges1alses herbe vented to atmosphere through: the conduits I I0 and I I 2. f 'finjoper'a'tiom pressurehfrorrfthe l'iead'er I0 is ommuni'cated through the'conduit I2l to the diaphragm Achamber llfand tends to move the upwardly. a majorfp'ortio'n of the in 'the dia- 4 weighted lever 86,'jwhile the remainder 'or the 'fore is `balanced by 'the' head iotmercurmgr'lother liquid, ln the conduits'98 and '|00 and the gaugeglasses `|02 and 'IM which eXlted agnst'the diafiforce resulting f romthe 'pressure previously defi This in turn.

noted that, dueito the Afact that not result in.' the upward of the mercury in 4 could be used in phragm 84.i 4In the event the steam pressure'inf creases, the pressure thereof 'exerted against the' diaphragm82 Vwill be increased and hence -willj pivoting of the arm 86." Thisjinturnfraises the diaphragm 94 and d is places mercury from the chamber .92 upwardly` into the gauge glasses. Inasmuch as the crossl' sectional area of diaphragm chamber 92 is sub-l stantially greater than the combined cross-'secs' tional areas ofthe two gauge glasses, this dis-f placement of mercury will-result in an increase in the head which is applied to th'diaphragm 94, thus balancing the increased pressure.----J-- i '1At the, sa me time,'the rise of4` mercury levelP in the glass |04 interrupts the beam of light from the source-44 to the photo-electric cell 40, which actuates arelay which in turn 'causes' a reversible motor, similar to the 'motor 64 shownin 1,"to rotate in the" proper direction 'to move th earm 26 upwardly? This in turnraises the photo-electric cell and the lightsorce until the beam is above the'mercuj'y'level, whereupon the motor 'stopsQ ,As was thecasein Fig. y1;-ifi the regulation resulting fromA 'this upward move" ment of the rod 281s suiiicient to arrest the'in' crease inthesteam pressure, no further' regula# tion takes place. However,` if the pressure con` tinues to rise,`fthis raises still further the level the gauge glass with the'result' that therod 2 6'is In theevent of a decrease in pressure, the arm 88 moves downwardly, thus permitting thev dia-i phragm 94 to move downwardly so that mercurs1 Vchamber i i2. `The resulting decrease in: level in' the gauge glass |02 permits light !romth'e source 46 t o 4strike 'the photo-electric cell 42, thus caus' ing/the motor tooperatejinthe direction-t6 lower the mazel .51 rifizhf c; .2 The luse oi. two'parallel gaugezglasse's in this' embodiment is merely for the'p'u'rpose of making it possible to separatethetwo photo-electric cells further from each other, thus eliminating all possibility of o'e cell being'aflected by the light source'intended for the othericelh 'Obvi` ously, the lsingle gauge glassshown' in Fig, \l couldbeemployed in the embodiment illustrated in Fig. A2', While the dual glasses shown in Fig. 2 any of the'other embodiments In Fig. 3 a, major portionrof the pressure is balanced by means of a trapped body of gas, such as air, while fluctuations inv pressure are'bal anced bychanges in liquid head In this emi bodiment the conduit I 2 communicates with the upper end of a gauge 'glass I8, while the lower end ot the 'glass is jconnected bymeans of a conduit I8 with a well I I6 formed in the bottom i.' Aa pressure vessel I I8.'?'This vessel may be charged with air up to the'desired pressure by means ofan air compressor I20 through a' conduit' |22 provided with a shut-oir valvefi24fand failpressue 'gauge |218. "'zr .A fnpaif of -photeiectiic seus and suitable light sources therefor are-*associatedv'with the Vgauge 'glass I8 *in exactly the same manner as shown in Fig. 1 and the photo-electric cells 'and "light sources arelraised and lowered by-"thesame'mech-` anismasfpreviously described. i* y Mercury, or other suitable liquid, i s place `d`n the gauge glass and well soas'to stand at "about the level indicated ,'and tfevessel` I I8 is "initially charged with air by means of the compressor |20 at' the same time that steamf'p're'ssure is admitted to the gauger by opening the valve Iliff-The vessel I I8 should be charged Ytoabout the s'ame'pressur moved upwardlyanother step'.l

as that normally existing in the header I0, and thereafter the valve |24 may be closed. Under these conditions, the mercury does not have to balance any of the steam pressure, and consequently the surface of the mercury in the glass I6 and in the well ||6 will stand at about the same level.

An increase in pressure will depress the level in the glass and raise it in the well until the difference in liquid head balances the increase in pressure. The chamber I I8 is made with sumcient volume so that the increase in pressure therein resulting from the decrease in air volume caused by the increase in level in the well II 6 will be negligible. Consequently, the variation in liquid level in the gauge will be proportionate to the variation in steam pressure, and this change.

in level may be employed to operate the reversible motor by means of the photo-electric cells in exactly the same manner as described in connection with Fig. 1.

In Fig. 4 the major portion of the steam pressure is balanced by means of a weighted bellows, so that again the mercury head need be suilicient only to balance variations in pressure` In this embodiment the conduit I2 connects the header I with a pressure vessel |30 in which is located a collapsible bellows |32. The lower end of this bellows is fixed to the bottom of the vessel |30, while the upper end is pivotally connected by means of a link |34 with a lever |35 which is pivoted at |38. This lever carries a weight |40, the lever and weight preferably being located within the vessel |30 in order to avoid the necessity of stufng boxes.

The interior of the bellows |32 is connected by means of a conduit |42 with the lower end of the gauge glass I6. the upper end of which may be vented to atmosphere through the conduit |44. The bellows is lled with mercury or other suitable liquid, which also fills the conduit |42 and the glass I6 up to about the level shown. When the steam is admitted to the vessel |30 through the conduit I2, the pressure thereof is exerted against the exterior of the bellows, thus tending to collapse the latter. This is resisted bythe weighted arm |36, which tends to expand the bellows, the weight and its position on the lever arm being so chosen as to balance the normal pressure of the steam. Should the steam pressure increase, it collapses the bellows |32, thus forcing mercury therefrom into the gauge glass I6, which raises the level in the glass. This increases the head of the mercury which acts to prevent collapse of the bellows, thus balancing the increase in steam pressure. The variation in liquid level in the gauge glass I6 may be utilized to control the light sources for a pair of photoelectric cells in the same manner as described in the previous embodiments.

In Fig. is shown an embodiment employing magnetically actuated switching means. The header I0 is connected through a conduit I2 with the upper end of a chamber I6, the lower end of which is connected to a conduit I8 having an atmospheric leg 20, as was the case in Fig. 1. Disposed within the chamber |6 is a magnet |50 constructed so as to float on the mercury or other liquid therein.

The rod 26 which is arranged to be moved vertically by the reversible motor 64 acting through gearing similar to that shown in Fig. 1, carries an arm |52. A bracket |54 is pivoted at |56 on this arm and carries a mercury switch |58. As is well known, tilting of a switch of this type to angle as shown with respect to the horizontal interrupts the circuit therethrough, while swinging it to a more nearly horizontal position, as by clockwise rotation of the bracket |54. completes the circuit through the switch. Secured to the lower end of bracket |54 is an arcuate member |60 made of magnetic material which, when the bracket is pivoted in a clockwise direction to a substantial vertical position embraces the chamber I6.

Arm |52 is extended to the opposite side of the chamber I6 and is formed with a downwardly extending portion |62 to which is pivoted a bracket |64. Secured to this bracket is a mercury switch |66. As is shown in Fig. 5, when the bracket |64 is substantially vertical the switch |66 is tilted to an angle which causes the mercury contained therein to interrupt the circuit through the switch. Secured to the lower end of the bracket |64 is an arcuate magnetic member |68 which is similar to member |60.

The reversible motor 64 is supplied with electric current through the lead 'I0 and 16. One branch of the lead 'I8 is connected through the mercury switch |58 to the terminal 12 lof the motor, while the other branch of this lead is connected through the switch |66 to the terminal 14. Obviously relay circuits, such as shown in Fig. 1, could be employedl if it is not desired to connect the power circuit through the mercury switches. However, relays are not necessary liecause switches of this nature are capable of car- 'rying suiiiciently heavy current to operate the motor. 1

The above described embodiment operates as follows. Pressure existing in the main I0 is communicated through the conduit I2 to the chamber I6, and this pressure is balanced by the column of mercury in the atmospheric leg 20. As previously described, the magnet |50 oats in the mercury in the chamber i6, and consequently is moved up and down as the level therein changesin response to variations of pressure. With the parts in the position shown in Fig. 5, the magnet |50 is below the magnetic member |60 on the bracket I 54 and consequently the bracket occupies the position shown, that is swung out from the chamber I6. This maintains the switch |58 in the tilted position so that the circuit therethrough is open. On the other hand, the magnet |50 is opposite the magnetic member |68 on the bracket I 64, and consequently the member |68 is attracted towards the chamber I6 so as to maintain the bracket |64 substantially vertical and hence the switch |66 is maintained in the tilted position in which the circuit therethrough is open. Consequently, no current is supplied to the motor 64 and the system is idle.

Assuming the pressure in the main I0 to decrease, the liquid level in the chamber I6 rises and consequently the magnet |50 is moved upwardly. When it comes opposite the magnetic member |60, the latter is attracted thereby so as to pivot the bracket |54 to a substantial vertical position, thus tilting the mercury switch |58 to a substantial horizontal position in` which the circuit therethrough is completed. l.At the same time the lower part of the magnet |60 is still opposite the magnetic member |68, and the latter thus remains attracted by the magnet |50 and hence no change takes place in the circuit through the switch |66. The closing of the switch |58 supplies the motor 64 with current through the terminals 68 and l2, thus causing the motor to operatein the proper direction to raise the rod 26. Inasmuch as the arm |52 is secured to this rod, the brackets |54 and |64 are likewise raised until the magnetic member |60 is lifted above the top of the magnet |50. Thereupon, the bracket |54 swings away from -the chamber i6 so as to tilt the switch |58 to open position, and the motor is stopped. As described in connection with the previous embodiments, if this amount of movement of the rod 26 does not provide suiiicient regulation to arrest the decrease in pressure. the magnet |50 is raised further so as to again close the switch |58, thus repeating the operation. In this way step-by-step regulation is obtained which minimizes hunting.

If the pressure in the main I increases, the liquid level and hence the magnet |50 falls until the latter is below the magnet member |68. Consequently, the bracket |64 pivots in a clockwise direction, thus turning the switch |66 to a substantially horizontal position in which the circuit therethrough is completed. This supplies current to the motor 64 through the terminals 68 and 14, causing the motor to operate in the opposite direction so as to move the rod 26 downwardly. When the magnetic member IL|68 is moved down to a position opposite the magnet |50 the switch |66 is again closed and, if necessary, the operation is repeated in the same manner as described in connection with a decrease in pressure.

Obviously, the magnetic switch means shown in Fig. could be used with any of the arrangements illustrated in Figs. 2 through 4 :for reducing the height of the atmospheric leg.

While I have shown and described several more or less specific embodiments of my invention, it is to be understood that this has been done for purposes of illustration only and that the scope of my invention is not to be limited thereby but is to be determined from the appended claims.

What is claimed:

1. In an automatic device operative by variations in fluid pressure. a first diaphragm, means for applying said pressure to said diaphragm, a weight acting on said diaphragm to balance a constant part of said pressure, a second diaphragm, a diaphragm chamber therefor, means for transferring movement of said rst diaphragm resulting from variations of said pressure to said second diaphragm, hollow means containing liquid connected to and extending above said diaphragm chamber, the cross-sectional area of said hollow means being less than that of said second diaphragm, a pair of electric switching means spaced vertically outside said hollow means and responsive to variations in the transmission of energy through said hollow means, means responsive to an increase inthe level of the liquid in said hollow means for varying the transmission of energy to the upper of '10 said switching means and responsive to a decrease in said level for varying the transmission of energy to the lower of said switching means, a reversible electric motor connected to be operated in one direction under the control of one of said switching means and in the opposite direction under the control of the other switching means. and means driven by said motor for moving said switching means relative to said hollow means in the same direction as the direction of movement of the liquid level which resulted in the operation of the motor.

2. In an automatic device operative by variations in iiuid pressure, a first diaphragm, means for applying said pressure to one side of said diaphragm, a pivotally mounted generally horizontal weighted lever, means for applying force from said lever to the other side of said diaphragm, a second diaphragm, a diaphragm chamber therefor, mechanical means for transferring movement of said iirst diaphragm to said second diaphragm, hollow means containing liquid connected to and extending above said chamber, the cross-sectional area of said chamber being greater than that of said hollow means, a pair of electric switching means spaced vertically outside said hollow means and responsive to variations in the transmission of energy through said hollow means, means responsive to an increase in the level of the liquid in said hollow means for varying the transmission of energy to the upper of said switching means and responsive to a decrease in said level for varying the transmission c of energy to the lower of said switching means, a

reversible electric motor connected to be operated in one direction under the control of one of said switching means and in the opposite direction under the control of the other switching means, and means driven by said motor for moving said switching means relative to said hollow means in the same direction as the direction of movement of the liquid which resulted in the operation of the motor.

GERALD S. CARRICK.

REFERENCES CITED The following references are of record in the OTHER REFERENCES Electronics Magazine, April 1944, pages 230, 232 and 234 article entitled Photo tube for Biological Recording. 

